Solid electrolytic capacitor for use in high voltage and high temperature applications

ABSTRACT

A capacitor assembly for use in high voltage and high temperature environments is provided. More particularly, the capacitor assembly includes a solid electrolytic capacitor element containing an anode body, a dielectric overlying the anode, and a solid electrolyte overlying the dielectric. To help facilitate the use of the capacitor assembly in high voltage applications, it is generally desired that the solid electrolyte is formed from a dispersion of preformed conductive polymer particles. In this manner, the electrolyte may remain generally free of high energy radicals (e.g., Fe 2+ or Fe 3+ ions) that can lead to dielectric degradation, particularly at relatively high voltages (e.g., above about 60 volts). Furthermore, to help protect the stability of the solid electrolyte at high temperatures, the capacitor element is enclosed and hermetically sealed within a housing in the presence of a gaseous atmosphere that contains an inert gas.

BACKGROUND OF THE INVENTION

Electrolytic capacitors (e.g., tantalum capacitors) are increasinglybeing used in the design of circuits due to their volumetric efficiency,reliability, and process compatibility. For example, one type ofcapacitor that has been developed is a solid electrolytic capacitor thatincludes an anode (e.g., tantalum), a dielectric oxide film (e.g.,tantalum pentoxide, Ta₂O₅) formed on the anode, a solid electrolytelayer, and a cathode. The solid electrolyte layer may be formed from aconductive polymer, such as described in U.S. Pat. No. 5,457,862 toSakata, et al., U.S. Pat. No. 5,473,503 to Sakata, et al., U.S. Pat. No.5,729,428 to Sakata, et al., and U.S. Pat. No. 5,812,367 to Kudoh, etal. Unfortunately, however, the stability of such solid electrolytes ispoor at high temperatures due to the tendency to transform from a dopedto an undoped state, or vice versa. As such, a need currently exists fora solid electrolytic capacitor having improved performance in hightemperature environments.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a capacitorassembly is disclosed that comprises a capacitor element comprising ananode formed from an anodically oxidized, sintered porous body and asolid electrolyte overlying the anode. The solid electrolyte is formedfrom a dispersion of conductive polymer particles. The assembly alsocomprises a housing that defines an interior space within which thecapacitor element is positioned, wherein the housing defines an interiorspace that has a gaseous atmosphere that contains an inert gas. An anodetermination is in electrical connection with the anode body and acathode termination that is in electrical connection with the solidelectrolyte.

In accordance with another embodiment of the present invention, a methodof forming a capacitor assembly is disclosed that comprises forming acapacitor element by a method that comprises anodically oxidizing asintered porous body to form an anode and applying a dispersion ofconductive polymer particles to the anode to form a solid electrolyte;positioning the capacitor element within an interior space of thehousing; electrically connecting the anode of the capacitor element toan anode termination and the solid electrolyte of the capacitor elementto a cathode termination; and hermetically sealing the capacitor elementwithin the housing in the presence of a gaseous atmosphere that containsan inert gas.

Other features and aspects of the present invention are set forth ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended figures in which:

FIG. 1 is a cross-sectional view of one embodiment of a capacitorassembly of the assembly of the present invention;

FIG. 2 is a perspective view of a leadframe in electrical connectionwith a capacitor in accordance with one embodiment of the presentinvention;

FIG. 3 is a cross-sectional view of a sintered anode body that may beemployed in one embodiment of the present invention; and

FIGS. 4-5 schematically illustrate one embodiment of a sintering methodthat may be employed in the present invention.

Repeat use of references characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstruction.

Generally speaking, the present invention is directed to a capacitorassembly for use in high voltage and high temperature environments. Moreparticularly, the capacitor assembly includes a solid electrolyticcapacitor element containing an anode body, a dielectric overlying theanode, and a solid electrolyte overlying the dielectric. To helpfacilitate the use of the capacitor assembly in high voltageapplications, it is generally desired that the solid electrolyte isformed from a dispersion of preformed conductive polymer particles. Inthis manner, the electrolyte may remain generally free of high energyradicals (e.g., Fe²⁺ or Fe³⁺ ions) that can lead to dielectricdegradation, particularly at relatively high voltages (e.g., above about60 volts). Furthermore, to help protect the stability of the solidelectrolyte at high temperatures, the capacitor element is enclosed andhermetically sealed within a housing in the presence of a gaseousatmosphere that contains an inert gas. It is believed that the housingand inert gas atmosphere are capable of limiting the amount of oxygenand moisture supplied to the conductive polymer of the capacitor. Inthis manner, the solid electrolyte is less likely to undergo a reactionin high temperature environments, thus increasing the thermal stabilityof the capacitor assembly. In addition to functioning well in both highvoltage and high temperature environments, the capacitor assembly of thepresent invention may also exhibit a high volumetric efficiency.

Various embodiments of the present invention will now be described inmore detail.

I. Capacitor Element

To help achieve the desired volumetric efficiency, the capacitor elementmay be formed in a manner so that it occupies a substantial portion ofthe volume of the interior space of the housing, such as about 30 vol. %or more, in some embodiments about 50 vol. % or more, in someembodiments about 60 vol. % or more, in some embodiments about 70 vol. %or more, in some embodiments from about 80 vol. % to about 98 vol. %,and in some embodiments, from about 85 vol. % to 97 vol. % of theinterior space of the housing. The ability to employ a capacitor elementthat has a size large enough to occupy a substantial portion of theinterior of a housing, such as described above, may be facilitated byoptimizing the dimensional stability of the anode. More specifically,selective control over the materials and method from which the anode ismade can allow it to remain dimensionally stable even after sintering.For example, the anode contains a porous body formed from a valve metalpowder. The specific charge of the powder may vary, such as from about2,000 μF*V/g to about 80,000 μF*V/g, in some embodiments from about5,000 μF*V/g to about 40,000 μF*V/g or more, and in some embodiments,from about 10,000 to about 20,000 μF*V/g. The valve metal powdercontains a valve metal (i.e., metal that is capable of oxidation) orvalve metal-based compound, such as tantalum, niobium, aluminum,hafnium, titanium, alloys thereof, oxides thereof, nitrides thereof, andso forth. For example, the valve metal composition may contain anelectrically conductive oxide of niobium, such as niobium oxide havingan atomic ratio of niobium to oxygen of 1:1.0±1.0, in some embodiments1:1.0±0.3, in some embodiments 1:1.0±0.1, and in some embodiments,1:1.0±0.05. For example, the niobium oxide may be NbO_(0.7), NbO_(1.0),NbO_(1.1), and NbO₂. Examples of such valve metal oxides are describedin U.S. Pat. No. 6,322,912 to Fife; U.S. Pat. No. 6,391,275 to Fife etal.; U.S. Pat. No. 6,416,730 to Fife et al.; U.S. Pat. No. 6,527,937 toFife; U.S. Pat. No. 6,576,099 to Kimmel, et al.; U.S. Pat. No. 6,592,740to Fife, et at; and U.S. Pat. No. 6,639,787 to Kimmel, et al.; and U.S.Pat. No. 7,220,397 to Kimmel, et al., as well as U.S. Patent ApplicationPublication Nos. 2005/0019581 to Schnitter; 2005/0103638 to Schnitter,et al.; 2005/0013765 to Thomas, et al., all of which are incorporatedherein in their entirety by reference thereto for all purposes.

The particles of the powder may be flaked, angular, nodular, andmixtures or variations thereof. The particles also typically have ascreen size distribution of at least about 60 mesh, in some embodimentsfrom about 60 to about 325 mesh, and in some embodiments, from about 100to about 200 mesh. Further, the specific surface area is from about 0.1to about 10.0 m²/g, in some embodiments from about 0.5 to about 5.0m²/g, and in some embodiments, from about 1.0 to about 2.0 m²/g. Theterm “specific surface area” refers to the surface area determined bythe physical gas adsorption (B.E.T.) method of Bruanauer, Emmet, andTeller, Journal of American Chemical Society, Vol. 60, 1938, p. 309,with nitrogen as the adsorption gas. Likewise, the bulk (or Scott)density is typically from about 0.1 to about 5.0 g/cm³, in someembodiments from about 0.2 to about 4.0 g/cm³, and in some embodiments,from about 0.5 to about 3.0 g/cm³.

Other components may be added to the powder to facilitate theconstruction of the anode body. For example, a binder and/or lubricantmay be employed to ensure that the particles adequately adhere to eachother when pressed to form the anode body. Suitable binders may includecamphor, stearic and other soapy fatty acids, Carbowax (Union Carbide),Glyptal (General Electric), polyvinyl alcohols, naphthalene, vegetablewax, and microwaxes (purified paraffins). The binder may be dissolvedand dispersed in a solvent. Exemplary solvents may include water,alcohols, and so forth. When utilized, the percentage of binders and/orlubricants may vary from about 0.1% to about 8% by weight of the totalmass. It should be understood, however, that binders and lubricants arenot required in the present invention.

The resulting powder may be compacted using any conventional powderpress mold. For example, the press mold may be a single stationcompaction press using a die and one or multiple punches. Alternatively,anvil-type compaction press molds may be used that use only a die andsingle lower punch. Single station compaction press molds are availablein several basic types, such as cam, toggle/knuckle and eccentric/crankpresses with varying capabilities, such as single action, double action,floating die, movable platen, opposed ram, screw, impact, hot pressing,coining or sizing. After compaction, the resulting anode body may thenbe diced into any desired shape, such as square, rectangle, circle,oval, triangle, hexagon, octagon, heptagon, pentagon, etc. The anodebody may also have a “fluted” shape in that it contains one or morefurrows, grooves, depressions, or indentations to increase the surfaceto volume ratio to minimize ESR and extend the frequency response of thecapacitance. The anode body may then be subjected to a heating step inwhich most, if not all, of any binder/lubricant are removed. Forexample, the anode body is typically heated by an oven that operates ata temperature of from about 150° C. to about 500° C. Alternatively, thebinder/lubricant may also be removed by contacting the pellet with anaqueous solution, such as described in U.S. Pat. No. 6,197,252 toBishop, et al.

Once formed, the anode body is then sintered. The temperature,atmosphere, and time of the sintering may depend on a variety offactors, such as the type of anode, the size of the anode, etc.Typically, sintering occurs at a temperature of from about from about800° C. to about 1900° C., in some embodiments from about 1000° C. toabout 1500° C., and in some embodiments, from about 1100° C. to about1400° C., for a time of from about 5 minutes to about 100 minutes, andin some embodiments, from about 30 minutes to about 60 minutes. Ifdesired, sintering may occur in an atmosphere that limits the transferof oxygen atoms to the anode. For example, sintering may occur in areducing atmosphere, such as in a vacuum, inert gas, hydrogen, etc. Thereducing atmosphere may be at a pressure of from about 10 Torr to about2000 Torr, in some embodiments from about 100 Torr to about 1000 Torr,and in some embodiments, from about 100 Torr to about 930 Torr. Mixturesof hydrogen and other gases (e.g., argon or nitrogen) may also beemployed.

Due to the specific charge of the powder used to form the anode body,sintering can sometimes result in a substantial degree of shrinkage. Asthe size of the anode body increases, this shrinkage can cause a fairlysignificant degree of bending in the anode structure. Without intendingto be limited by theory, it is believed that bending is increased whenthe anode body is in physical contact with external hard surface(s)(e.g., surface of a sinter tray). More specifically, such hard surfacescan limit shrinkage of the anode body at those locations where physicalcontact exists (sometimes referred to as “pinning”) and thereby resultin less shrinkage at the area of physical contact than other locationsof the anode body. This shrinkage differential can, in turn, cause theanode body to bend and form a curved shape (e.g., crescent shape). Tominimize such bending, sintering may be performed in such a manner thatthe surfaces of the anode body are not in physical contact with anexternal surface (e.g., surface of a sintering tray).

Referring to FIGS. 4-5, for example, one embodiment of such a sinteringtechnique is shown in which one or more anodes 20 are connected to astringer 200 via an anode lead 42. Any known method may be employed toattach the anode lead 42 to the stringer 200, such as welding, swaging,etc. In this manner, the anodes 20 are able to “hang” from the stringer200 without physically contacting an external surface. The resultinganode assembly 201 may thus be positioned on a surface 221 that passesthrough a heat treatment device or furnace 220 (FIG. 5). As the anodes20 are heated in the furnace 220, they are allowed to shrink freelywithout physical constraint. It should also be understood that variousother configurations may be employed for sintering an anode without suchconstraint. In another embodiment, for instance, a hanging anode may bevertically displaced into a furnace and then lifted out of the deviceupon completion of the sintering process.

Despite its relatively large size, the resulting anode may thus remaindimensionally stable in that it possesses only a small degree ofcurvature, if any. The dimensional stability may be characterized by theorientation of the anode relative to a longitudinal medial plane thatextends through an end of the anode. Referring to FIG. 3, for example,one embodiment of an anode 20 is shown that extends in the direction ofa longitudinal axis 3. The anode 20 has an upper end portion 17 andlower end portion 19 between which extends a first edge portion 7 and anopposing second edge portion 9. A medial longitudinal plane 13 extendsthrough the upper end portion 17 in a direction parallel to thelongitudinal axis 3. Due to its dimensional stability, the anode 20possesses only a small surface variance, if any, between the medialplane 13 and respective edge portions 7 and 9. That is, the difference“W” between the distance “a” (between the medial plane 13 and the edgeportion 7) and the distance “b” (between the medial plane 13 and theedge portion 9), also known as “warp”, is generally small along thelength of the anode 20. For example, the difference W (or “warp”) may beabout 0.25 millimeters or less, in some embodiments about 0.20millimeters or less, in some embodiments about 0.15 millimeters or less,and in some embodiments, from 0 to about 0.10 millimeters, along thelength of the anode 20, such as at the center of the anode as shown inFIG. 3.

The radius of curvature, which is inversely proportional to the degreeof curvature, may also be used to define the dimensionally stable anode20. The radius of curvature may be specified in a direction that isrepresentative of the general shape of the anode 20, such as in thedirection of a medial transverse plane 14 that is perpendicular to themedial longitudinal plane 13. More particularly, the radius of curvatureis represented by the designation “R” in FIG. 3, and may be calculatedby the equation: Radius=W/2+L²/8W, wherein W is the “warp” describedabove and L is the length. In certain embodiments, the radius ofcurvature in the direction of the medial transverse plane 14 may beabout 25 centimeters or greater, in some embodiments about 50centimeters or greater, and in some embodiments, about 100 centimetersor greater.

An anode lead may also be connected to the anode body that extends in alongitudinal direction therefrom. The anode lead may be in the form of awire, sheet, etc., and may be formed from a valve metal compound, suchas tantalum, niobium, niobium oxide, etc. Connection of the lead may beaccomplished using known techniques, such as by welding the lead to thebody or embedding it within the anode body during formation (e.g., priorto compaction and/or sintering).

As indicated above, the anode is also coated with a dielectric. Thedielectric may be formed by anodically oxidizing (“anodizing”) thesintered anode so that a dielectric layer is formed over and/or withinthe anode. For example, a tantalum (Ta) anode may be anodized totantalum pentoxide (Ta₂O₅). Typically, anodization is performed byinitially applying a solution to the anode, such as by dipping anodeinto the electrolyte. A solvent is generally employed, such as water(e.g., deionized water). To enhance ionic conductivity, a compound maybe employed that is capable of dissociating in the solvent to form ions.Examples of such compounds include, for instance, acids, such asdescribed below with respect to the electrolyte. For example, an acid(e.g., phosphoric acid) may constitute from about 0.01 wt. % to about 5wt. %, in some embodiments from about 0.05 wt. % to about 0.8 wt. %, andin some embodiments, from about 0.1 wt. % to about 0.5 wt. % of theanodizing solution. If desired, blends of acids may also be employed.

A current is passed through the anodizing solution to form thedielectric layer. The value of the formation voltage manages thethickness of the dielectric layer. For example, the power supply may beinitially set up at a galvanostatic mode until the required voltage isreached. Thereafter, the power supply may be switched to apotentiostatic mode to ensure that the desired dielectric thickness isformed over the entire surface of the anode. Of course, other knownmethods may also be employed, such as pulse or step potentiostaticmethods. The voltage at which anodic oxidation occurs typically rangesfrom about 4 to about 250 V, and in some embodiments, from about 9 toabout 200 V, and in some embodiments, from about 20 to about 150 V.During oxidation, the anodizing solution can be kept at an elevatedtemperature, such as about 30° C. or more, in some embodiments fromabout 40° C. to about 200° C., and in some embodiments, from about 50°C. to about 100° C. Anodic oxidation can also be done at ambienttemperature or lower. The resulting dielectric layer may be formed on asurface of the anode and within its pores.

As indicated above, a solid electrolyte overlies the dielectric thatgenerally functions as the cathode for the capacitor. The solidelectrolyte may be formed from one or more conductive polymer layers.The conductive polymer(s) employed in such layers are typicallyπ-conjugated and have electrical conductivity after oxidation orreduction, such as an electrical conductivity of at least about 1 μScm⁻¹ after oxidation. Examples of such π-conjugated conductive polymersinclude, for instance, polyheterocycles (e.g., polypyrroles,polythiophenes, polyanilines, etc.), polyacetylenes, poly-p-phenylenes,polyphenolates, and so forth. Particularly suitable conductive polymersare substituted polythiophenes having the following general structure:

wherein,

T is O or S;

D is an optionally substituted C₁ to C₅ alkylene radical (e.g.,methylene, ethylene, n-propylene, n-butylene, n-pentylene, etc.);

R₇ is a linear or branched, optionally substituted C₁ to C₁₈ alkylradical (e.g., methyl, ethyl, n- or iso-propyl, n-, iso-, sec- ortert-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl,1-ethylpropyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl,2,2-dimethylpropyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl,n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-hexadecyl,n-octadecyl, etc.); optionally substituted C₅ to C₁₂ cycloalkyl radical(e.g., cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononylcyclodecyl, etc.); optionally substituted C₆ to C₁₄ aryl radical (e.g.,phenyl, naphthyl, etc.); optionally substituted C₇ to C₁₈ aralkylradical (e.g., benzyl, o-, m-, p-tolyl, 2,3-, 2,4-, 2,5-, 2-6,3-4-,3,5-xylyl, mesityl, etc.); optionally substituted C₁ to C₄ hydroxyalkylradical, or hydroxyl radical; and

q is an integer from 0 to 8, in some embodiments, from 0 to 2, and inone embodiment, 0; and

n is from 2 to 5,000, in some embodiments from 4 to 2,000, and in someembodiments, from 5 to 1,000. Example of substituents for the radicals“D” or “R₇” include, for instance, alkyl, cycloalkyl, aryl, aralkyl,alkoxy, halogen, ether, thioether, disulphide, sulfoxide, sulfone,sulfonate, amino, aldehyde, keto, carboxylic acid ester, carboxylicacid, carbonate, carboxylate, cyano, alkylsilane and alkoxysilanegroups, carboxylamide groups, and so forth.

Particularly suitable thiophene polymers are those in which “D” is anoptionally substituted C₂ to C₃ alkylene radical. For instance, thepolymer may be optionally substituted poly(3,4-ethylenedioxythiophene),which has the following general structure:

Methods for forming conductive polymers, such as described above, arewell known in the art. For instance, U.S. Pat. No. 6,987,663 to Merker,et al., which is incorporated herein in its entirety by referencethereto for all purposes, describes various techniques for formingsubstituted polythiophenes from a monomeric precursor. The monomericprecursor may, for instance, have the following structure:

wherein,

T, D, R₇, and q are defined above. Particularly suitable thiophenemonomers are those in which “D” is an optionally substituted C₂ to C₃alkylene radical. For instance, optionally substituted3,4-alkylenedioxythiophenes may be employed that have the generalstructure:

wherein, R₇ and q are as defined above. In one particular embodiment,“q” is 0. One commercially suitable example of 3,4-ethylenedioxthiopheneis available from H.C. Starck GmbH under the designation Clevios™ M.Other suitable monomers are also described in U.S. Pat. No. 5,111,327 toBlohm, et al. and U.S. Pat. No. 6,635,729 to Groenendaal, et al., whichare incorporated herein in their entirety by reference thereto for allpurposes. Derivatives of these monomers may also be employed that are,for example, dimers or trimers of the above monomers. Higher molecularderivatives, i.e., tetramers, pentamers, etc. of the monomers aresuitable for use in the present invention. The derivatives may be madeup of identical or different monomer units and used in pure form and ina mixture with one another and/or with the monomers. Oxidized or reducedforms of these precursors may also be employed.

The thiophene monomers are chemically polymerized in the presence of anoxidative catalyst. The oxidative catalyst may be a transition metalsalt, such as a salt of an inorganic or organic acid that containammonium, sodium, gold, iron(III), copper(Il), chromium(VI), cerium(IV),manganese(IV), manganese(VII), or ruthenium(III) cations. Particularlysuitable transition metal salts include halides (e.g., FeCl₃ or HAuCl₄);salts of other inorganic acids (e.g., Fe(ClO₄)₃, Fe₂(SO₄)₃, (NH₄)₂S₂O₈,or Na₃Mo₁₂PO₄₀); and salts of organic acids and inorganic acidscomprising organic radicals. Examples of salts of inorganic acids withorganic radicals include, for instance, iron(III) salts of sulfuric acidmonoesters of C₁ to C₂₀ alkanols (e.g., iron(III) salt of laurylsulfate). Likewise, examples of salts of organic acids include, forinstance, iron(III) salts of C₁ to C₂₀ alkane sulfonic acids (e.g.,methane, ethane, propane, butane, or dodecane sulfonic acid); iron (III)salts of aliphatic perfluorosulfonic acids (e.g., trifluoromethanesulfonic acid, perfluorobutane sulfonic acid, or perfluorooctanesulfonic acid); iron (III) salts of aliphatic C₁ to C₂₀ carboxylic acids(e.g., 2-ethylhexylcarboxylic acid); iron (III) salts of aliphaticperfluorocarboxylic acids (e.g., trifluoroacetic acid or perfluorooctaneacid); iron (III) salts of aromatic sulfonic acids optionallysubstituted by C₁ to C₂₀ alkyl groups (e.g., benzene sulfonic acid,o-toluene sulfonic acid, p-toluene sulfonic acid, or dodecylbenzenesulfonic acid); iron (III) salts of cycloalkane sulfonic acids (e.g.,camphor sulfonic acid); and so forth. Mixtures of these above-mentionedsalts may also be used.

If desired, polymerization of the monomer may occur in a precursorsolution. Solvents (e.g., polar protic or non-polar) may be employed inthe solution, such as water, glycols (e.g., ethylene glycol, propyleneglycol, butylene glycol, triethylene glycol, hexylene glycol,polyethylene glycols, ethoxydiglycol, dipropyleneglycol, etc.); glycolethers (e.g., methyl glycol ether, ethyl glycol ether, isopropyl glycolether, etc.); alcohols (e.g., methanol, ethanol, n-propanol,iso-propanol, and butanol); ketones (e.g., acetone, methyl ethyl ketone,and methyl isobutyl ketone); esters (e.g., ethyl acetate, butyl acetate,diethylene glycol ether acetate, methoxypropyl acetate, ethylenecarbonate, propylene carbonate, etc.); amides (e.g., dimethylformamide,dimethylacetamide, dimethylcaprylic/capric fatty acid amide andN-alkylpyrrolidones); sulfoxides or sulfones (e.g., dimethyl sulfoxide(DMSO) and sulfolane); phenolic compounds (e.g., toluene, xylene, etc.),and so forth. Water is a particularly suitable solvent for the reaction.When employed, the total amount of solvents in the precursor solutionmay be from about 40 wt. % wt. % to about 90 wt. %, in some embodimentsfrom about 50 wt. % to about 85 wt. %, and in some embodiments, fromabout 60 wt. % to about 80 wt. %.

Polymerization of the thiophene monomer generally occurs at atemperature of from about 10° C. to about 100° C., and in someembodiments, from about 15° C. to about 75° C. Upon completion of thereaction, known filtration techniques may be employed to remove any saltimpurities. One or more washing steps may also be employed to purify thedispersion.

Upon polymerization, the resulting conductive polymer is generally inthe form of particles having a small size, such as an average diameterof from about 1 to about 200 nanometers, in some embodiments from about2 to about 100 nanometers, and in some embodiments, from about 4 toabout 50 nanometers. The diameter of the particles may be determinedusing known techniques, such as by ultracentrifuge, laser diffraction,etc. The shape of the particles may likewise vary. In one particularembodiment, for instance, the particles are spherical in shape. However,it should be understood that other shapes are also contemplated by thepresent invention, such as plates, rods, discs, bars, tubes, irregularshapes, etc. The concentration of the particles in the dispersion mayvary depending on the desired viscosity of the dispersion and theparticular manner in which the dispersion is to be applied to thecapacitor. Typically, however, the particles constitute from about 0.1to about 10 wt. %, in some embodiments from about 0.4 to about 5 wt. %,and in some embodiments, from about 0.5 to about 4 wt. % of thedispersion.

If desired, the formation of the conductive polymer into a particulateform may be enhanced by using a separate counterion to counteract acharged conductive polymer (e.g., polythiophene). That is, theconductive polymer (e.g., polythiophene or derivative thereof) used inthe solid electrolyte typically has a charge on the main polymer chainthat is neutral or positive (cationic). Polythiophene derivatives, forinstance, typically carry a positive charge in the main polymer chain.In some cases, the polymer may possess positive and negative charges inthe structural unit, with the positive charge being located on the mainchain and the negative charge optionally on the substituents of theradical “R”, such as sulfonate or carboxylate groups. The positivecharges of the main chain may be partially or wholly saturated with theoptionally present anionic groups on the radicals “R.” Viewed overall,the polythiophenes may, in these cases, be cationic, neutral or evenanionic. Nevertheless, they are all regarded as cationic polythiophenesas the polythiophene main chain has a positive charge.

The counterion may be a monomeric or polymeric anion. Polymeric anionscan, for example, be anions of polymeric carboxylic acids (e.g.,polyacrylic acids, polymethacrylic acid, polymaleic acids, etc.);polymeric sulfonic acids (e.g., polystyrene sulfonic acids (“PSS”),polyvinyl sulfonic acids, etc.); and so forth. The acids may also becopolymers, such as copolymers of vinyl carboxylic and vinyl sulfonicacids with other polymerizable monomers, such as acrylic acid esters andstyrene. Likewise, suitable monomeric anions include, for example,anions of C₁ to C₂₀ alkane sulfonic acids (e.g., dodecane sulfonicacid); aliphatic perfluorosulfonic acids (e.g., trifluoromethanesulfonic acid, perfluorobutane sulfonic acid or perfluorooctane sulfonicacid); aliphatic C₁ to C₂₀ carboxylic acids (e.g.,2-ethyl-hexylcarboxylic acid); aliphatic perfluorocarboxylic acids(e.g., trifluoroacetic acid or perfluorooctanoic acid); aromaticsulfonic acids optionally substituted by C₁ to C₂₀ alkyl groups (e.g.,benzene sulfonic acid, o-toluene sulfonic acid, p-toluene sulfonic acidor dodecylbenzene sulfonic acid); cycloalkane sulfonic acids (e.g.,camphor sulfonic acid or tetrafluoroborates, hexafluorophosphates,perchlorates, hexafluoroantimonates, hexafluoroarsenates orhexachloroantimonates); and so forth. Particularly suitablecounteranions are polymeric anions, such as a polymeric carboxylic orsulfonic acid (e.g., polystyrene sulfonic acid (“PSS”)). The molecularweight of such polymeric anions typically ranges from about 1,000 toabout 2,000,000, and in some embodiments, from about 2,000 to about500,000.

When employed, the weight ratio of such counterions to conductivepolymers in a given layer of the solid electrolyte is typically fromabout 0.5:1 to about 50:1, in some embodiments from about 1:1 to about30:1, and in some embodiments, from about 2:1 to about 20:1. The weightof the electrically conductive polymers corresponds referred to theabove-referenced weight ratios refers to the weighed-in portion of themonomers used, assuming that a complete conversion occurs duringpolymerization.

In addition to conductive polymer(s) and optional counterion(s), thedispersion may also contain one or more binders to further enhance theadhesive nature of the polymeric layer and also increase the stabilityof the particles within the dispersion. The binders may be organic innature, such as polyvinyl alcohols, polyvinyl pyrrolidones, polyvinylchlorides, polyvinyl acetates, polyvinyl butyrates, polyacrylic acidesters, polyacrylic acid amides, polymethacrylic acid esters,polymethacrylic acid amides, polyacrylonitriles, styrene/acrylic acidester, vinyl acetate/acrylic acid ester and ethylene/vinyl acetatecopolymers, polybutadienes, polyisoprenes, polystyrenes, polyethers,polyesters, polycarbonates, polyurethanes, polyamides, polyimides,polysulfones, melamine formaldehyde resins, epoxide resins, siliconeresins or celluloses. Crosslinking agents may also be employed toenhance the adhesion capacity of the binders. Such crosslinking agentsmay include, for instance, melamine compounds, masked isocyanates orfunctional silanes, such as 3-glycidoxypropyltrialkoxysilane,tetraethoxysilane and tetraethoxysilane hydrolysate or crosslinkablepolymers, such as polyurethanes, polyacrylates or polyolefins, andsubsequent crosslinking.

Dispersion agents may also be employed to facilitate the formation ofthe solid electrolyte and the ability to apply it to the anode part.Suitable dispersion agents include solvents, such as aliphatic alcohols(e.g., methanol, ethanol, i-propanol and butanol), aliphatic ketones(e.g., acetone and methyl ethyl ketones), aliphatic carboxylic acidesters (e.g., ethyl acetate and butyl acetate), aromatic hydrocarbons(e.g., toluene and xylene), aliphatic hydrocarbons (e.g., hexane,heptane and cyclohexane), chlorinated hydrocarbons (e.g.,dichloromethane and dichloroethane), aliphatic nitriles (e.g.,acetonitrile), aliphatic sulfoxides and sulfones (e.g., dimethylsulfoxide and sulfolane), aliphatic carboxylic acid amides (e.g.,methylacetamide, dimethylacetamide and dimethylformamide), aliphatic andaraliphatic ethers (e.g., diethylether and anisole), water, and mixturesof any of the foregoing solvents. A particularly suitable dispersionagent is water.

In addition to those mentioned above, still other ingredients may alsobe used in the dispersion. For example, conventional fillers may be usedthat have a size of from about 10 nanometers to about 100 micrometers,in some embodiments from about 50 nanometers to about 50 micrometers,and in some embodiments, from about 100 nanometers to about 30micrometers. Examples of such fillers include calcium carbonate,silicates, silica, calcium or barium sulfate, aluminum hydroxide, glassfibers or bulbs, wood flour, cellulose powder carbon black, electricallyconductive polymers, etc. The fillers may be introduced into thedispersion in powder form, but may also be present in another form, suchas fibers.

Surface-active substances may also be employed in the dispersion, suchas ionic or non-ionic surfactants. Furthermore, adhesives may beemployed, such as organofunctional silanes or their hydrolysates, forexample 3-glycidoxypropyltrialkoxysilane, 3-aminopropyl-triethoxysilane,3-mercaptopropyl-trimethoxysilane, 3-metacryloxypropyltrimethoxysilane,vinyltrimethoxysilane or octyltriethoxysilane. The dispersion may alsocontain additives that increase conductivity, such as ethergroup-containing compounds (e.g., tetrahydrofuran), lactonegroup-containing compounds (e.g., γ-butyrolactone or γ-valerolactone),amide or lactam group-containing compounds (e.g., caprolactam,N-methylcaprolactam, N,N-dimethylacetamide, N-methylacetamide,N,N-dimethylformamide (DMF), N-methylformamide, N-methylformanilide,N-methylpyrrolidone (NMP), N-octylpyrrolidone, or pyrrolidone), sulfonesand sulfoxides (e.g., sulfolane(tetramethylenesulfone) ordimethylsulfoxide (DMSO)), sugar or sugar derivatives (e.g., saccharose,glucose, fructose, or lactose), sugar alcohols (e.g., sorbitol ormannitol), furan derivatives (e.g., 2-furancarboxylic acid or3-furancarboxylic acid), an alcohols (e.g., ethylene glycol, glycerol,di- or Methylene glycol).

The polymeric dispersion may be applied by to the part using a varietyof known techniques, such as by spin coating, impregnation, pouring,dropwise application, injection, spraying, doctor blading, brushing,printing (e.g., ink-jet, screen, or pad printing), or dipping. Althoughit may vary depending on the application technique employed, theviscosity of the dispersion is typically from about 0.1 to about 100,000mPas (measured at a shear rate of 100 s⁻¹), in some embodiments fromabout 1 to about 10,000 mPas, in some embodiments from about 10 to about1,500 mPas, and in some embodiments, from about 100 to about 1000 mPas.Once applied, the layer may be dried and washed.

One benefit of employing such a dispersion is that it may be able topenetrate into the edge region of the capacitor body to increase theadhesion to the dielectric. This results in a more mechanically robustpart, which may reduce equivalent series resistance and leakage current.Such dispersions may also minimize the presence of ionic species (e.g.,Fe²⁺ or Fe³⁺) produced during in situ polymerization, which can causedielectric breakdown under high electric field due to ionic migration.Thus, by applying the conductive polymer as a dispersion rather throughin situ polymerization, the resulting capacitor may exhibit a relativelyhigh “breakdown voltage” (voltage at which the capacitor fails), such asabout 60 volts or more, in some embodiments about 80 volts or more, insome embodiments about 100 volts or more, and in some embodiments, fromabout 120 volts to about 200 volts, as determined by increasing theapplied voltage in increments of 3 volts until the leakage currentreaches 1 mA.

If desired, the solid electrolyte may be formed from one or multiplelayers. When multiple layers are employed, it is possible that one ormore of the layers includes a conductive polymer formed by in situpolymerization. However, when it is desired to achieve very highbreakdown voltages (e.g., from about 120 to 200 volts), the presentinventors have discovered that the solid electrolyte is formed primarilyfrom the polymeric dispersions described above, and that it is generallyfree of conductive polymers formed via in situ polymerization.Regardless of the number of layers employed, the resulting solidelectrolyte typically has a total a thickness of from about 1 micrometer(μm) to about 200 μm, in some embodiments from about 2 μm to about 50μm, and in some embodiments, from about 5 μm to about 30 μm.

The solid electrolyte may optionally be healed upon application to theanode part. Healing may occur after each application of a solidelectrolyte layer or may occur after the application of the entirecoating if multiple layers are employed. In some embodiments, forexample, the solid electrolyte may be healed by dipping the pellet intoan electrolyte solution, such as a solution of acid, and thereafterapplying a constant voltage to the solution until the current is reducedto a preselected level. If desired, such healing may be accomplished inmultiple steps. After application of some or all of the layers describedabove, the resulting part may then be washed if desired to removevarious byproducts, excess oxidizing agents, and so forth. Further, insome instances, drying may be utilized after some or all of the dippingoperations described above. For example, drying may be desired afterapplying the oxidizing agent and/or after washing the pellet in order toopen the pores of the part so that it can receive a liquid duringsubsequent dipping steps.

The part may optionally be applied with one or more additional layers,such as an external coating that overlies the solid electrolyte. Theexternal coating may contain at least one carbonaceous layer and atleast one metal layer that overlies the carbonaceous layer. The metallayer may act as a solderable conductor, contact layer, and/or chargecollector for the capacitor, and may be formed from a conductive metal,such as copper, nickel, silver, nickel, zinc, tin, palladium, lead,copper, aluminum, molybdenum, titanium, iron, zirconium, magnesium, andalloys thereof. Silver is a particularly suitable conductive metal foruse in the layer. The carbonaceous layer may limit contact between themetal layer and the solid electrolyte, which would otherwise increasethe resistance of the capacitor. The carbonaceous layer may be formedfrom a variety of known carbonaceous materials, such as graphite,activated carbon, carbon black, etc. The thickness of the carbonaceouslayer is typically within the range of from about 1 μm to about 50 μm,in some embodiments from about 2 μm to about 30 μm, and in someembodiments, from about 5 μm to about 10 μm. Likewise, the thickness ofthe metal layer is typically within the range of from about 1 μm toabout 100 μm, in some embodiments from about 5 μm to about 50 μm, and insome embodiments, from about 10 μm to about 25 μm.

A protective coating may also be employed between the dielectric and thesolid electrolyte. The protective coating may include a relativelyinsulative resinous material (natural or synthetic). Such materials mayhave a specific resistivity of greater than about 10 Ω·cm, in someembodiments greater than about 100, in some embodiments greater thanabout 1,000 Ω·cm, in some embodiments greater than about 1×10⁵ Ω·cm, andin some embodiments, greater than about 1×10¹⁰ Ω·cm. Some resinousmaterials that may be utilized in the present invention include, but arenot limited to, polyurethane, polystyrene, esters of unsaturated orsaturated fatty acids (e.g., glycerides), and so forth. For instance,suitable esters of fatty acids include, but are not limited to, estersof lauric acid, myristic acid, palmitic acid, stearic acid, eleostearicacid, oleic acid, linoleic acid, linolenic acid, aleuritic acid,shellolic acid, and so forth. These esters of fatty acids have beenfound particularly useful when used in relatively complex combinationsto form a “drying oil”, which allows the resulting film to rapidlypolymerize into a stable layer. Such drying oils may include mono-, di-,and/or tri-glycerides, which have a glycerol backbone with one, two, andthree, respectively, fatty acyl residues that are esterified. Forinstance, some suitable drying oils that may be used include, but arenot limited to, olive oil, linseed oil, castor oil, tung oil, soybeanoil, and shellac. These and other protective coating materials aredescribed in more detail U.S. Pat. No. 6,674,635 to Fife, et al., whichis incorporated herein in its entirety by reference thereto for allpurposes.

Although not necessarily required, it is often desired that thecapacitor element is generally free of resinous encapsulants (e.g.,epoxy resin) often used in solid electrolytic capacitors. Among otherthings, such resinous materials can lead to a reduction in volumetricefficiency of the capacitor assembly.

II. Housing

The capacitor element of the present invention is enclosed andhermetically sealed within a housing. Hermetic sealing typically occursin the presence of a gaseous atmosphere that contains at least one inertgas so as to inhibit oxidation of the solid electrolyte during use. Theinert gas may include, for instance, nitrogen, helium, argon, xenon,neon, krypton, radon, and so forth, as well as mixtures thereof.Typically, inert gases constitute the majority of the atmosphere withinthe housing, such as from about 50 wt. % to 100 wt. %, in someembodiments from about 75 wt. % to 100 wt. %, and in some embodiments,from about 90 wt. % to about 99 wt. % of the atmosphere. If desired, arelatively small amount of non-inert gases may also be employed, such ascarbon dioxide, oxygen, water vapor, etc. In such cases, however, thenon-inert gases typically constitute 15 wt. % or less, in someembodiments 10 wt. % or less, in some embodiments about 5 wt. % or less,in some embodiments about 1 wt. % or less, and in some embodiments, fromabout 0.01 wt. % to about 1 wt. % of the atmosphere within the housing.For example, the moisture content (expressed in terms of relativelyhumidity) may be about 10% or less, in some embodiments about 5% orless, in some embodiments about 1% or less, and in some embodiments,from about 0.01 to about 5%.

Any of a variety of different materials may be used to form the housing,such as metals, plastics, ceramics, and so forth. In one embodiment, forexample, the housing includes one or more layers of a metal, such astantalum, niobium, aluminum, nickel, hafnium, titanium, copper, silver,steel (e.g., stainless), alloys thereof (e.g., electrically conductiveoxides), composites thereof (e.g., metal coated with electricallyconductive oxide), and so forth. In another embodiment, the housing mayinclude one or more layers of a ceramic material, such as aluminumnitride, aluminum oxide, silicon oxide, magnesium oxide, calcium oxide,glass, etc., as well as combinations thereof.

The housing may have any desired shape, such as cylindrical, D-shaped,rectangular, triangular, prismatic, etc. Referring to FIGS. 1-2, forexample, one embodiment of a capacitor assembly 100 is shown thatcontains a housing 122 and a capacitor element 120, which includes ananode 140 and a solid electrolyte layer 160 overlying the anode 140. Inthis particular embodiment, the housing 122 is generally rectangular.Typically, the housing and the capacitor element have the same orsimilar shape so that the capacitor element can be readily accommodatedwithin the interior space. In the illustrated embodiment, for example,both the capacitor element 120 and the housing 122 have a generallyrectangular shape.

As indicated above, the capacitor assembly of the present invention mayexhibit a relatively high volumetric efficiency. To facilitate such highefficiency, the capacitor element typically occupies a substantialportion of the volume of an interior space of the housing. For example,the capacitor element may occupy about 30 vol. % or more, in someembodiments about 50 vol. % or more, in some embodiments about 60 vol. %or more, in some embodiments about 70 vol. % or more, in someembodiments from about 80 vol. % to about 98 vol. %, and in someembodiments, from about 85 vol. % to 97 vol. % of the interior space ofthe housing. To this end, the difference between the dimensions of thecapacitor element and those of the interior space defined by the housingare typically relatively small.

Referring to FIGS. 1-2, for example, the capacitor element 120 of FIGS.1-2 has a length that is defined between edge portions 177 and 179(excluding the length of the anode lead 6). Likewise, the interior space126 has a length that is defined between interior surfaces of first andsecond edge portions 107 and 109, respectively. Typically, the ratio ofthe length of the anode to the length of the interior space ranges fromabout 0.40 to 1.00, in some embodiments from about 0.50 to about 0.99,in some embodiments from about 0.60 to about 0.99, and in someembodiments, from about 0.70 to about 0.98. For example, the capacitorelement 120 may have a length of from about 5 to about 10 millimeters,and the interior space 126 may have a length of from about 6 to about 15millimeters. Similarly, the ratio of the height of the capacitor element120 (in the −z direction) to the height of the interior space 126 mayrange from about 0.40 to 1.00, in some embodiments from about 0.50 toabout 0.99, in some embodiments from about 0.60 to about 0.99, and insome embodiments, from about 0.70 to about 0.98. The ratio of the widthof the capacitor element 120 (in the −x direction) to the width of theinterior space 126 may also range from about 0.50 to 1.00, in someembodiments from about 0.60 to about 0.99, in some embodiments fromabout 0.70 to about 0.99, in some embodiments from about 0.80 to about0.98, and in some embodiments, from about 0.85 to about 0.95. Forexample, the width of the capacitor element 120 may be from about 2 toabout 7 millimeters and the width of the interior space 126 may be fromabout 3 to about 10 millimeters, and the height of the capacitor element120 may be from about 0.5 to about 2 millimeters and the width of theinterior space 126 may be from about 0.7 to about 6 millimeters.

Generally, the capacitor element is attached to the housing in such amanner that an anode termination and cathode termination are formedexternal to the housing for subsequent integration into a circuit. Theparticular configuration of the terminations may depend on the intendedapplication. In one embodiment, terminal pins may be employed thatextend through opposing ends of the housing. Referring again to FIG. 1,for instance, one of the terminal pins (not shown) may be connected(e.g., welded) to the anode lead 6 so that it extends through a wall 124of the housing, while another of the terminal pins (not shown) isconnected to the cathode of the capacitor element 120 and extendsthrough a wall 124.

While a terminal pin configuration may be useful in certain embodiments,the present inventors have discovered that the capacitor assembly mayalso be formed so that it is surface mountable, and yet stillmechanically robust. For example, the anode lead may be electricallyconnected to external, surface mountable anode and cathode terminations(e.g., pads, sheets, plates, frames, etc.). Such terminations may extendthrough the housing to connect with the capacitor. The thickness orheight of the terminations is generally selected to minimize thethickness of the capacitor assembly. For instance, the thickness of theterminations may range from about 0.05 to about 1 millimeter, in someembodiments from about 0.05 to about 0.5 millimeters, and from about 0.1to about 0.2 millimeters. If desired, the surface of the terminationsmay be electroplated with nickel, silver, gold, tin, etc. as is known inthe art to ensure that the final part is mountable to the circuit board.In one particular embodiment, the termination(s) are deposited withnickel and silver flashes, respectively, and the mounting surface isalso plated with a tin solder layer. In another embodiment, thetermination(s) are deposited with thin outer metal layers (e.g., gold)onto a base metal layer (e.g., copper alloy) to further increaseconductivity.

In certain embodiments, connective members may be employed within theinterior space of the housing to facilitate connection to theterminations in a mechanically stable manner. For example, referringagain to FIGS. 1-2, the capacitor assembly 100 may include a connectionmember 162 that is formed from a first portion 167 and a second portion165. The connection member 162 may be formed from conductive materialssimilar to the external terminations. The first portion 167 and secondportion 165 may be integral or separate pieces that are connectedtogether, either directly or via an additional conductive element (e.g.,metal). In the illustrated embodiment, the second portion 165 isprovided in a plane that is generally parallel to a longitudinaldirection in which the lead 6 extends (e.g., −y direction). The firstportion 167 is “upstanding” in the sense that it is provided in a planethat is generally perpendicular the longitudinal direction in which thelead 6 extends. In this manner, the first portion 167 can limit movementof the lead 6 in the horizontal direction to enhance surface contact andmechanical stability during use.

The first portion 167 may also possess a mounting region 151 (see FIG.2) that is connected to an anode lead 6. The region 151 may have a“U-shape” for further enhancing surface contact and mechanical stabilityof the lead 6. Connection of the region 151 to the lead 6 may beaccomplished using any of a variety of known techniques, such aswelding, laser welding, conductive adhesives, etc. In one particularembodiment, for example, the region 151 is laser welded to the anodelead 6. Regardless of the technique chosen, however, the first portion167 can hold the anode lead 6 in substantial horizontal alignment tofurther enhance the dimensional stability of the capacitor assembly 100.

Referring again to FIG. 1, one embodiment of the present invention isshown in which the connective member 162 and capacitor element 120 areconnected to the housing 122 through anode and cathode terminations 127and 129, respectively. More specifically, the housing 122 includes alower wall 122 and two opposing sidewalls 124 between which a cavity 126is formed that includes the capacitor element 120. The lower wall 122and sidewalls 124 may be formed from one or more layers of a metal,plastic, or ceramic material such as described above. In this particularembodiment, the anode termination 127 contains a first region 127 a thatis positioned within the housing 122 and electrically connected to theconnection member 162 and a second region 127 b that is positionedexternal to the housing 122 and provides a mounting surface 201.Likewise, the cathode termination 129 contains a first region 129 a thatis positioned within the housing 122 and electrically connected to thesolid electrolyte of the capacitor element 120 and a second region 129 bthat is positioned external to the housing 122 and provides a mountingsurface 203. It should be understood that the entire portion of suchregions need not be positioned within or external to the housing.

More specifically and as further shown in FIG. 1, the first region ofthe cathode termination is disposed between a first sidewall and thelower wall, forms a part of the housing, and defines a portion of theinterior space in which the capacitor element is housed. Similarly, thefirst region of the anode termination is disposed between an opposingsecond sidewall and the lower wall, forms a part of the housing, anddefines a portion of the interior space in which the capacitor elementis housed.

Connection of the terminations 127 and 129 may be made using any knowntechnique, such as welding, laser welding, conductive adhesives, etc. Inone particular embodiment, for example, a conductive adhesive 131 isused to connect the second portion 165 of the connection member 162 tothe anode termination 127. Likewise, a conductive adhesive 133 is usedto connect the cathode of the capacitor element 120 to the cathodetermination 129. The conductive adhesives may be formed from conductivemetal particles contained with a resin composition. The metal particlesmay be silver, copper, gold, platinum, nickel, zinc, bismuth, etc. Theresin composition may include a thermoset resin (e.g., epoxy resin),curing agent (e.g., acid anhydride), and coupling agent (e.g., silanecoupling agents). Suitable conductive adhesives are described in U.S.Patent Application Publication No. 2006/0038304 to Osako, et al., whichis incorporated herein in its entirety by reference thereto for allpurposes.

Of course, other techniques may also be employed to connect theterminations. In alternative embodiments, for example, the terminationsmay be connected to the housing via conductive traces that extendthrough the housing. Any conductive material may be employed to form thetraces, such as a conductive metal (e.g., copper, nickel, silver, zinc,tin, palladium, lead, copper, aluminum, molybdenum, titanium, iron,zirconium, tungsten, magnesium, and alloys thereof). Particularlysuitable conductive metals include, for instance, copper, copper alloys(e.g., copper-zirconium, copper-magnesium, copper-zinc, or copper-iron),nickel, and nickel alloys (e.g., nickel-iron). The traces may be formedusing any known technique, such as by printing or coating an inkcontaining the metal onto a surface of the housing. Various techniquesfor providing conductive traces in a housing are described in moredetail in U.S. Pat. No. 5,314,606 to Irie, et al. and U.S. Pat. No.7,304,832 to Ushio, et al., as well as U.S. Patent ApplicationPublication No. 2005/0167789 to Zhuanq and 2007/0138606 to Brailey, allof which are incorporated herein in their entirety by reference theretofor all purposes.

Regardless of the manner in which the terminations are connected, theresulting package is hermetically sealed as described above. Referringto FIG. 1, for instance, the housing 122 may also include a lid 125 thatis placed on an upper surface of the side walls 124 after the capacitorelement 120 is positioned within the housing 122. The lid 125 may beformed from a ceramic, metal (e.g., iron, copper, nickel, cobalt, etc.,as well as alloys thereof), plastic, and so forth. In one embodiment,for example, the lid contains a Kovar® alloy (Carpenter TechnologyCorporation), which is a nickel-cobalt ferrous alloy. The size of thehousing 122 is generally such that the lid 125 does not contact anysurface of the capacitor element 120 so that it is not contaminated.When placed in the desired position, the lid 125 is hermetically sealedto the sidewalls 124 using known techniques, such as welding (e.g.,resistance welding, laser welding, etc.), soldering, etc. Hermeticsealing generally occurs in the presence of inert gases as describedabove so that the resulting assembly is substantially free of reactivegases, such as oxygen or water vapor.

Although not required, other layers and/or materials may also beemployed in the housing 122. For example, one or more barrier members(not shown) may be formed on the lower wall 122, sidewall(s) 124, and/orlid 125 to inhibit damage to the capacitor element 120 during hermeticsealing of the assembly. The barrier member(s) may be formed from anymaterials known in the art, such as antireflection materials that arecapable of preventing a laser beam from being reflected. Examples ofsuch materials may include polymers, such as epoxy resins, polyimides,polyolefins (e.g., polyethylene or polypropylene), optionally containingfiller particles (e.g., black pigment).

As a result of the present invention, the capacitor assembly may exhibitexcellent electrical properties even when exposed to high temperatureenvironments. For example, the capacitor assembly may have anequivalence series resistance (“ESR”) of less than about 50 ohms, insome embodiments less than about 25 ohms, in some embodiments from about0.01 to about 10 ohms, and in some embodiments, from about 0.05 to about5 ohms, measured at an operating frequency of 100 Hz. In addition, theleakage current, which generally refers to the current flowing from oneconductor to an adjacent conductor through an insulator, can bemaintained at relatively low levels. For example, the numerical value ofthe normalized leakage current of a capacitor of the present inventionis, in some embodiments, less than about 1 μA/μF*V, in some embodimentsless than about 0.5 μA/μF*V, and in some embodiments, less than about0.1 μA/μF*V, where μA is microamps and μF*V is the product of thecapacitance and the rated voltage. Such ESR and normalized leakagecurrent values may even be maintained after aging for a substantialamount of time at high temperatures. For example, the values may bemaintained for about 100 hours or more, in some embodiments from about300 hours to about 3000 hours, and in some embodiments, from about 400hours to about 2500 hours (e.g., 500 hours, 600 hours, 700 hours,800hours, 900 hours, 1000 hours, 1100 hours, 1200 hours, or 2000 hours)at temperatures ranging from about 100° C. to about 250° C., and, insome embodiments from about 100° C. to about 225° C., and in someembodiments, from about 100° C. to about 225° C. and in someembodiments, from about 100° C. to about 225° C. (e.g., 100° C., 125°C., 150° C., 175° C., or 200° C.).

The capacitor may also exhibit a high energy density that enables itsuitable for use in high pulse applications. Energy density is generallydetermined according to the equation E=½*CV², where C is the capacitancein farads (F) and V is the working voltage of capacitor in volts (V).The capacitance may, for instance, be measured using a capacitance meter(e.g., Keithley 3330 Precision LCZ meter with Kelvin Leads, 2 volts biasand 1 volt signal) at an operating frequency of 120 Hz and a temperatureof 25° C. For example, the capacitor may exhibit an energy density ofabout 2.0 joules per cubic centimeter (J/cm³) or more, in someembodiments about 3.0 J/cm³, in some embodiments from about 4.0 J/cm³ toabout 10.0 J/cm³, and in some embodiments, from about 4.5 to about 8.0J/cm³. The capacitance may likewise be about 1 milliFarad per squarecentimeter (“mF/cm²”) or more, in some embodiments about 2 mF/cm² ormore, in some embodiments from about 5 to about 50 mF/cm², and in someembodiments, from about 8 to about 20 mF/cm².

The present invention may be better understood by reference to thefollowing examples.

Test Procedures

Leakage Current:

Leakage current (“DCL”) was measured using a leakage test set thatmeasures leakage current at a temperature of 25° C. and at the ratedvoltage after a minimum of 20 seconds.

Capacitance

The capacitance was measured using a Keithley 3330 Precision LCZ meterwith Kelvin Leads with 2.2 volt DC bias and a 0.5 volt peak to peaksinusoidal signal. The operating frequency was 120 Hz and thetemperature was 23° C.±2° C.

Equivalent Series Resistance (ESR)

Equivalence series resistance may be measured using a Keithley 3330Precision LCZ meter with Kelvin Leads 2.2 volt DC bias and a 0.5 voltpeak to peak sinusoidal signal. The operating frequency was 100 kHz andthe temperature was 23° C.±2° C.

EXAMPLE 1

A tantalum anode with a size of 5.2 mm (length)×3.7 mm (width)×0.85 mm(height) was anodized at 120V in a liquid electrolyte to 10 μF, Aconductive polymer coating was then formed by dipping the anode into adispersed poly(3,4-ethylenedioxythiophene) having a solids content 1.1%(Clevios™ K, H.C. Starck). Upon coating, the part was then dried at 125°C. for 20 minutes. This process was repeated 6 times. Thereafter, thepart was dipped into a dispersed poly(3,4-ethylenedioxythiophene) havinga solids content 2% and dried at 125° C. for 20 minutes. Once again,this process was repeated 6 times. External carbon and silver coats wereformed for finishing the manufacturing process of the anodes.

A standard copper-based leadframe was used to finish the assemblyprocess. One portion of the leadframe was attached to the lower surfaceof the capacitor element with a silver adhesive. The tantalum wire ofthe capacitor element was then laser welded to another portion of theleadframe.

Ceramic housings were also obtained Kyocera America, Inc. of San Diego,Calif. under the name “Cap Pak.” The housing had an interior length of9.0 mm, a width of 4.0 mm, and a height of 1.5 mm with gold platedsolder pads on the bottom inside part of ceramic housing. The lead framewas first glued to a gold anode termination inside the container andthereafter the cathode portion of the capacitor was glued to a goldcathode termination. The adhesive employed for the terminations weresilver-loaded epoxy adhesives). The resulting assembly was then heatedin a convection oven preset at 150° C. for 60 minutes to cure theadhesive. After curing, a Kovar® metal lid having a length of 9.95 mm, awidth of 4.95 mm, and a thickness of 0.10 mm was placed over the top ofthe container, closely on the seal ring of the ceramic housing (Kovar®ring having a thickness of 0.30 mm) so that there was no direct contactbetween the interior surface of the lid and the exterior surface of theattached capacitor. The resulting assembly was placed into a weldingchamber and purged with nitrogen gas for 120 minutes before seam weldingbetween seal ring and the lid was performed. No additional burn-in orhealing was performed after the seam welding.

EXAMPLE 2

A tantalum anode with a size of 1.8 mm×2.4 mm×1.2 mm was anodized at 16Vin a liquid electrolyte to 150 μF. A conductive polymer coating was thenformed by dipping the anode into a butanol solution of iron (III)toluenesulfonate (Clevios™ C, H.C. Starck) for 5 minutes andconsequently into 3,4-ethylenedioxythiophene (Clevios™ M, H.C. Starck)for 1 minute. After 45 minutes of polymerization, a thin layer ofpoly(3,4-ethylenedioxythiophene) was formed on the surface of thedielectric. The parts were washed in methanol to remove reactionby-products, anodized in a liquid electrolyte, and washed again inmethanol. The polymerization cycle was repeated 12 times. The parts werethen coated by graphite and silver and assembled into a ceramic housingas described in Example 1.

For life testing purposes, the parts of Examples 1 and 2 were placed inan oven at 125° C. (with an applied voltage equal to the rated voltage)and at 200° C. (with an applied voltage equal to 50% of the ratedvoltage). Parts were also placed in an oven at 215° C. and 230° C.(without applied voltage). After 500 hours of each tests, the leakagecurrent (DCL), equivalent series resistance (ESR), and capacitance ofthe parts were determined at room temperature (23° C.±2° C.) to verifywhether the part had shown any degradation. The results are set forthbelow in Tables 1 and 2.

TABLE 1 Life Testing at 125° C. or 200° C. (Applied Voltage) ConditionsBefore Testing After Testing Exam- Temp DCL CAP ESR DCL CAP ESR ple [°C.] Voltage [μA] [μF] [mΩ] [μA] [μF] [mΩ] 1 125 rated 5.8 8.2 143 0.68.2 138 200 50% of rated 22.0 8.3 128 55.4 8.1 171 2 125 rated 11.8138.0 172 82.9 134.4 268 200 50% of rated N/A

TABLE 2 Life Testing at 215° C. or 230° C. and No Applied VoltageConditions Before Testing After Testing Temp DCL CAP ESR DCL CAP ESRExample [° C.] Voltage [μA] [μF] [mΩ] [μA] [μF] [mΩ] 1 215 — 1.8 8.5 3671.8 9.0 383 230 — 0.3 8.4 327 0.6 9.0 353 2 215 — 53.6 144.0 68 18.943.1 8000 230 — 14.5 144.0 83 8.3 10.6 156000

As indicated in both tables, and particularly in Table 2, the ESR andleakage current of the samples formed with a dispersion of PEDTparticles (Example 1) was significantly lower after life testing thenthe samples formed with sequentially applied PEDT.

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

What is claimed is:
 1. A capacitor assembly comprising: a capacitorelement comprising an anode formed from an anodically oxidized, sinteredporous body and a solid electrolyte overlying the anode, wherein thesolid electrolyte is formed from a dispersion of conductive polymerparticles, wherein the conductive polymer particles have an averagediameter of from about 4 nanometers to about 50 nanometers, wherein thesolid electrolyte further comprises a polymeric counterion, and whereinthe solid electrolyte is generally free of conductive polymers formedvia in situ polymerization; a housing that defines an interior spacewithin which the capacitor element is positioned, wherein the interiorspace has a gaseous atmosphere that contains an inert gas, furtherwherein the housing comprises metal opposing first and second sidewallsand a metal lower wall; an anode termination that is in electricalconnection with the anode body; and a cathode termination that is inelectrical connection with the solid electrolyte, wherein the capacitorelement is hermetically sealed within the housing, wherein the capacitorassembly exhibits a breakdown voltage of about 60 volts or more.
 2. Thecapacitor assembly of claim 1, wherein the conductive polymer particlesinclude a substituted polythiophene having the following generalstructure:

wherein, T is 0 or S; D is an optionally substituted C₁ to C₅ alkyleneradical; R₇ is a linear or branched, optionally substituted C₁ to C₁₈alkyl radical; optionally substituted C₅ to C₁₂ cycloalkyl radical;optionally substituted C₆ to C₁₄ aryl radical; optionally substituted C₇to C₁₈ aralkyl radical; optionally substituted C₁ to C₄ hydroxyalkylradical, or hydroxyl radical; and q is an integer from 0 to 8; and n isfrom 2 to 5,000.
 3. The capacitor assembly of claim 2, wherein thesubstituted polythiophene has the following general structure:


4. The capacitor assembly of claim 1, wherein the conductive polymerparticles include poly(3,4-ethylenedioxythiophene).
 5. The capacitorassembly of claim 1, wherein the counterion includes a polystyrenesulfonic acid.
 6. The capacitor assembly of claim 1, wherein the solidelectrolyte further comprises a binder.
 7. The capacitor assembly ofclaim 1, wherein the porous body is formed from tantalum or niobiumoxide.
 8. The capacitor assembly of claim 1, wherein the sintered porousbody is dimensionally stable.
 9. The capacitor assembly of claim 1,wherein the ratio of the length of the anode to the length of theinterior space is from about 0.40 to about 1.00.
 10. The capacitorassembly of claim 1, wherein the ratio of the height of the anode to theheight of the interior space is from about 0.40 to about 1.00.
 11. Thecapacitor assembly of claim 1, wherein the ratio of the width of theanode to the width of the interior space is from about 0.80 to about0.99.
 12. The capacitor assembly of claim 1, wherein the housing and theanode have a generally rectangular shape.
 13. The capacitor assembly ofclaim 1, wherein the inert gas includes nitrogen, helium, argon, xenon,neon, krypton, radon, or combinations thereof.
 14. The capacitorassembly of claim 1, wherein inert gases constitute from about 50 wt.%to 100 wt.% of the gaseous atmosphere.
 15. The capacitor assembly ofclaim 1, wherein oxygen constitutes less than about 1 wt.% of thegaseous atmosphere.
 16. The capacitor assembly of claim 1, wherein theanode and cathode terminations are surface mountable.
 17. The capacitorassembly of claim 1, further comprising a lead that extends in alongitudinal direction from the porous body of the anode, wherein thelead is positioned within the interior space of the housing.
 18. Thecapacitor assembly of claim 17, further comprising a connective memberthat contains a first portion that is positioned generally perpendicularto the longitudinal direction of the anode lead and connected thereto.19. The capacitor assembly of claim 18, wherein the connective memberfurther contains a second portion that is generally parallel to thelongitudinal direction in which the anode lead extends.
 20. Thecapacitor assembly of claim 19, wherein the second portion is positionedwithin the housing.
 21. The capacitor assembly of claim 1, wherein ametal lid is welded or soldered to the metal opposing sidewalls.
 22. Thecapacitor assembly of claim 1, wherein the capacitor assembly exhibits abreakdown voltage of about 100 volts or more.
 23. The capacitor assemblyof claim 1, wherein the capacitor element is free of a resinousencapsulant.
 24. A method of forming a capacitor assembly, the methodcomprising: forming a capacitor element by a method that comprisesanodically oxidizing a sintered porous body to form an anode andapplying a dispersion of conductive polymer particles to the anode toform a solid electrolyte, wherein the conductive polymer particles havean average diameter of from about 4 nanometers to about 50 nanometers,wherein the solid electrolyte further comprise polymeric counterion, andwherein the solid electrolyte is generally free of conductive polymersformed by in situ polymerization; positioning the capacitor elementwithin an interior space of the housing, wherein the housing comprisesmetal opposing first and second sidewalls and a metal lower wall;electrically connecting the anode of the capacitor element to an anodetermination and the solid electrolyte of the capacitor element to acathode termination; and hermetically sealing the capacitor elementwithin the housing in the presence of a gaseous atmosphere that containsan inert gas, wherein the capacitor assembly exhibits a breakdownvoltage of about 60 volts or more.
 25. The method of claim 24, whereinthe anode is dipped into the dispersion.
 26. The method of claim 24,wherein the conductive polymer particles constitute from about 0.1 toabout 10 wt.% of the dispersion.
 27. The capacitor assembly of claim 1,wherein a first region of the anode termination is positioned within thehousing and wherein a second region of the anode termination ispositioned external to the housing.
 28. The capacitor assembly of claim1, wherein a first region of the cathode termination is positionedwithin the housing and wherein a second region of the cathodetermination is positioned external to the housing.
 29. The capacitorassembly of claim 1, wherein a dielectric layer is formed over theanode, further wherein the dispersion of conductive polymer particles isin direct contact with the dielectric layer.